We measured characteristics of thermal/pain (th/p) sensitivity of Helix albescens (threshold and latency of the avoidance behavioral reaction) under conditions of the hot-plate test. As was found, weakening (shielding) of the background electromagnetic field, as well as the action of low-intensity radiations of extremalfrequency ranges, induced two-phase changes of these characteristics within a 21-day-long observation period with different manifestations and durations of the phases. Initial increase in the nociceptive sensitivity (hyperalgesia) was followed by an analgesic effect with subsequent return of the examined indices to the initial level. Low-intensity electromagnetic influences also induced modifications of the infradian rhythmics of th/p sensitivity of the molluscs; this was manifested in changes of the spectra and phase shifts of the identified rhythms and trends toward modulation of the amplitudes of these rhythmic components.

We studied the role of the opioid system in the modulation of thermonociceptive sensitivity of Helix albestens mollusks subjected within a 21-day-long period to the conditions of electromagnetic shielding, action of a weak extremely low-frequency oscillating magnetic field, and combination of the above factors. Results of blocking of opioid receptors by naloxone demonstrated that the efficacy of antonociceptive influences of the opioid system is dissimilar within different stages of action of the above electromagnetic factors. We believe that changes in the activity of this system are involved, to a noticeable extent, in magnetoinduced modulation of thermonociceptive sensitivity in mollusks.

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